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International audience; Monilinia laxa is a fungus that causes brown rot in stone fruit. Immature green fruits in the first stage of fruit development (stage I) are generally susceptible. To investigate the relationship between the physical characteristics of immature fruit and susceptibility to M. laxa, we characterized the progeny, derived from a clone of wild peach (Prunus davidiana) crossed with two commercial nectarines (Prunus persica) varieties, through laboratory infection, transpiration monitoring and stomata counting. Two types of fruit infections were observed - ‘classic’ brown rot and ‘clear spot’ symptoms - which have not previously been described in the literature. The number and density of stomata did not explain the observed variability of infection in the progeny. However, surface conductance was positively correlated with infection level. This study provides experimental evidence partially linking physical fruit characteristics to brown rot infection at the immature fruit stage. The role of delayed cuticle deposition in susceptibility to brown rot of immature fruit is discussed.

Potassium (K) deficiency has consequences not only on cellular ion balance and transmembrane potential but also on metabolism. In fact, several enzymes are K-dependent including enzymes in catabolism, causing an alteration in glycolysis and respiration. In addition, K deficiency is associated with the induction of specific pathways and accumulation of metabolic biomarkers, such as putrescine. However, such drastic changes are usually observed when K deficiency is established. Here, we carried out a kinetic analysis with metabolomics to elucidate early metabolic events when nutrient conditions change from K-sufficiency to K-deficiency in Arabidopsis rosettes from both wild type and mutants affected in both K absorption and low-K signalling (hak5 akt1 cipk23). Our results show that mutants have a metabolomics pattern similar to K-deficient wild-type, showing a constitutive metabolic response to low K. In addition, shifting to low K conditions induces (i) changes in sugar metabolism and (ii) an accumulation of salicylic acid metabolites before the appearance of biomarkers of K deficiency (putrescine and aconitate), and such an accumulation is more pronounced in mutants. Our results suggest that early events in the response to low K conditions involve salicylic acid metabolism., G.T. thank the Région Pays de la Loire and Angers Loire Métropole for its financial support via the grant Connect Talent Isoseed. We thank Sergio García for his skilful assistance. This work was funded by grant number 20806/PI/18 (to FR) from Fundación Séneca de la Región de Murcia, Spain, grant PID2019-106649RB-I00 from Ministerio de Ciencia e Innovación, Spain (to FR and MN-C). This work was also supported by the Red de Excelencia BIO2016-81957-REDT from Ministerio de Economía, Industria y Competitividad. All grants from Spanish ministries were co-financed by the FEDER Fund. MN-C, is recipient of a Ramón y Cajal Fellowship (RyC-2017-21924) from Ministerio de Economía y Competitividad, Spain

Pemphigus is a life-threatening auto-immune blistering disease of the skin and mucous membrane that is caused by the production of auto-antibodies (auto-Abs) directed against adhesion proteins: desmoglein 1 and 3. We demonstrated in the "Ritux3" trial, the high efficacy of rituximab, an anti-CD20 recombinant monoclonal antibody, as the first-line treatment for pemphigus. However, 25% of patients relapsed during the six-month period after rituximab treatment. These early relapses were associated with a lower decrease in anti-desmoglein auto-Abs after the initial cycle of rituximab. The N-glycosylation of immunoglobulin-G (IgG) can affect their affinity for Fc receptors and their serum half-life. We hypothesized that the extended half-life of Abs could be related to modifications of IgG N-glycans. The IgG N-glycome from pemphigus patients and its evolution under rituximab treatment were analyzed. Pemphigus patients presented a different IgG N-glycome than healthy donors, with less galactosylated, sialylated N-glycans, as well as a lower level of N-glycans bearing an additional N-acetylglucosamine. IgG N-glycome from patients who achieved clinical remission was not different to the one observed at baseline. Moreover, our study did not identify the N-glycans profile as discriminating between relapsing and non-relapsing patients. We report that pemphigus patients present a specific IgG N-glycome. The changes observed in these patients could be a biomarker of autoimmunity susceptibility rather than a sign of inflammation. ispartof: BIOMEDICINES vol:10 issue:8 ispartof: location:Switzerland status: published

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International audience; Sharka disease, due to the Plum pox virus, is a major threat to apricot trees. Most of the accessions world-wide and particularly those cultivated in Western Europe and the Mediterranean area are susceptible to the disease. A few resistance sources have been identified to date in cultivars developed in the US from a basis of Central Asian germplasm, all of these sharing the same genomic region associated with resistance to sharka in chromosome 1. Based on this, Simple sequence repeats (SSR) markers framing the MATH genes possibly responsible for the resistance have been developed in this region and a set of 2 SSRs (PGS1.21 and PGS1.24) and an indel (ZP002) was selected for identifying and discarding susceptible individuals at the plantlet stage of the apricot breeding process. However SSR markers could be difficult to implement by small teams due to the investment in hands-on time and equipment. As a consequence we turned to single nucleotide polymorphisms (SNP) to develop an alternative set of markers that could be cheaper and more easily implemented. Taking advantage of the numerous apricot genomic-sequences available at the UGAFL, we identified resistant/susceptible SNP/indel haplotypes and developed a set of three primer triplets (SP353, SP870, and SP871) based on the competitive allele-specific PCR (KASP™) technique by LGC genomics. This set was validated using a wide range of apricot accessions from different geographic origins and genetic backgrounds, concurrently with the original set of three SSRs. The new set gave similar results as the SSR-based set, was more convenient and, as a result, is now routinely used for early selection of apricot seedlings in our breeding programs.

International audience; Breeding varieties for increased disease resistance is a major means to control epidemics. However, the deployment of resistance genes through space and time drives the genetic composition of the pathogen population, directionally altering pathotype frequencies. In France, Leptosphaeria maculans causes stem canker on Brassica napus oilseed rape crops but not on B. juncea condiment mustard. Prior to the deployment of winter B. napus varieties with Rlm6 resistance gene introduced fromB. juncea, the aim of our study was to investigate if this deployment could impact disease control in condiment mustard. We assessed the presence of resistance genes against the disease in a set of current FrenchB. juncea varieties and breeding lines with a set of five differential L. maculans isolates carrying know Avr/avr genes.Rlm6was detected in all 12 condiment mustard varieties.Rlm5was also detected in eight varieties. No additional resistance genes were detected with the set of isolates used. Because the frequency of isolates virulent onRlm6is very low in France, these results indicate thatRlm6gene is a major component of disease control in the French B. juncea mustards tested. Using Rlm6 in oilseed rape varieties will very likely induce an increase in frequency ofRlm6virulent isolates. This raises the acute concern of a wise deployment of oilseed rape around the condiment mustard growing area. Scientific knowledge on adaptation dynamics, spatial segregation of crops and cooperation between actors is currently available in order to mitigate the risk and advert negative consequences of the introduction ofRlm6resistance gene in oilseed rape varieties.

International audience; Nowadays, little information is available regarding the N‐glycosylation pathway in the green microalga Chlamydomonas reinhardtii. Recent investigation demonstrated that C. reinhardtii synthesizes linear oligomannosides. Maturation of these oligomannosides results in N‐glycans that are partially methylated and carry one or two xylose residues. One xylose residue was demonstrated to be a core β(1,2)‐xylose. Recently, N‐glycoproteomic analysis performed on glycoproteins secreted by C. reinhardtii demonstrated that the xylosyltransferase A (XTA) was responsible for the addition of the core β(1,2)‐xylose. Furthermore, another xylosyltransferase candidate named XTB was suggested to be involved in the xylosylation in C. reinhardtii. In the present study, we focus especially on the characterization of the structures of the xylosylated N‐glycans from C. reinhardtii taking advantage of insertional mutants of XTA and XTB, and of the XTA/XTB double‐mutant. The combination of mass spectrometry approaches allowed us to identify the major N‐glycan structures bearing one or two xylose residues. They confirm that XTA is responsible for the addition of the core β(1,2)‐xylose, whereas XTB is involved in the addition of the xylose residue onto the linear branch of the N‐glycan as well as in the partial addition of the core β(1,2)‐xylose suggesting that this transferase exhibits a low substrate specificity. Analysis of the double‐mutant suggests that an additional xylosyltransferase is involved in the xylosylation process in C. reinhardtii. Additional putative candidates have been identified in the C. reinhardtii genome. Altogether, these results pave the way for a better understanding of the C. reinhardtii N‐glycosylation pathway.

International audience; Cucumber vein yellowing virus (CVYV) is an emerging virus on cucurbits in the Mediterranean Basin, against which few resistance sources are available, particularly in melon. The melon accession PI 164323 displays complete resistance to isolate CVYV-Esp, and accession HSD 2458 presents a tolerance, i.e. very mild symptoms in spite of virus accumulation in inoculated plants. The resistance is controlled by a dominant allele Cvy-1 1 , while the tolerance is controlled by a recessive allele cvy-2, independent from Cvy-1 1 . Before introducing the resistance or tolerance in commercial cultivars through a long breeding process, it is important to estimate their specificity and durability. Upon inoculation with eight molecularly diverse CVYV isolates, the resistance was found to be isolate-specific since many CVYV isolates induced necrosis on PI 164323, whereas the tolerance presented a broader range. A resistance-breaking isolate inducing severe mosaic on PI 164323 was obtained. This isolate differed from the parental strain by a single amino acid change in the VPg coding region. An infectious CVYV cDNA clone was obtained, and the effect of the mutation in the VPg cistron on resistance to PI 164323 was confirmed by reverse genetics. This represents the first determinant for resistance-breaking in an ipomovirus. Our results indicate that the use of the Cvy-1 1 allele alone will not provide durable resistance to CVYV and that, if used in the field, it should be combined with other control methods such as cultural practices and pyramiding of resistance genes to achieve long-lasting resistance against CVYV.

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To date, it is widely accepted by the scientific community that many agricultural regions will experience more extreme temperature fluctuations. These stresses will undoubtedly impact crop production, particularly fruit and seed yields. In fact, pollination is considered as one of the most temperature-sensitive phases of plant development and until now, except for the time-consuming and costly processes of genetic breeding, there is no immediate alternative to address this issue. In this work, we used a multidisciplinary approach using physiological, biochemical, and molecular techniques for studying the effects of two carbohydrate-based natural activators on in vitro tomato pollen germination and pollen tube growth cultured in vitro under cold conditions. Under mild and strong cold temperatures, these two carbohydrate-based compounds significantly enhanced pollen germination and pollen tube growth. The two biostimulants did not induce significant changes in the classical molecular markers implicated in pollen tube growth. Neither the number of callose plugs nor the CALLOSE SYNTHASE genes expression were significantly different between the control and the biostimulated pollen tubes when pollens were cultivated under cold conditions. PECTIN METHYLESTERASE (PME) activities were also similar but a basic PME isoform was not produced or inactive in pollen grown at 8°C. Nevertheless, NADPH oxidase (RBOH) gene expression was correlated with a higher number of viable pollen tubes in biostimulated pollen tubes compared to the control. Our results showed that the two carbohydrate-based products were able to reduce in vitro the effect of cold temperatures on tomato pollen tube growth and at least for one of them to modulate reactive oxygen species production.

The skin epidermis is continuously exposed to external aggressions, including environmental pollution. The cosmetic industry must be able to offer dedicated products to fight the effects of pollutants on the skin. We set up an experimental model that exposed skin explants maintained in culture to a pollutant mixture. This mixture P representing urban pollution was designed on the basis of the French organization ‘Air Parif’ database. A chamber, called Pollubox®, was built to allow a controlled nebulization of P on the cultured human skin explants. We investigated ultrastructural morphology by transmission electron microscopy of high pressure frozen skin explants. A global transcriptomic analysis indicated that the pollutant mixture was able to induce relevant xenobiotic and antioxidant responses. Modulated detoxifying genes were further investigated by laser micro-dissection coupled to qPCR, and immunochemistry. Both approaches showed that P exposure correlated with overexpression of detoxifying genes and provoked skin physiological alterations down to the stratum basale. The model developed herein might be an efficient tool to study the effects of pollutants on skin as well as a powerful testing method to evaluate the efficacy of cosmetic products against pollution.

International audience; In eukaryots the protein N-glycosylation processes starts in the endoplasmic reticulum and continues with the maturation steps in the Golgi apparatus (Fig. 1). In C. reinhardtii, the maturation steps results in glycans N-linked to proteins ranging from Man5GlcNAc2 to Man3GlcNAc2 and carrying one or two xylose residues (Fig. 1) (Vanier et al. 2017, Lucas/Dumontier et al. 2018). Nowadays, little information is available regarding the xylosylation in C. reinhardtii. This study aimed at characterizing the molecular actors involved in xylosylation process using complementary analysis, such as Western blot, nanoliquid chromatography coupled to electrospray mass spectrometry (nanoLC-ESI-MS), multistage tandem mass spectrometry (ESI-MSn) and ion mobility spectrometry-tandem mass spectrometry (IMS-MS2), on xylosyltransferase insertional mutants.

International audience; Aphanomyces euteiches is an oomycete pathogen that causes the pea root rot. We investigated the potential role of early belowground defense in pea (susceptible plant) and faba bean (tolerant plant) at three days after inoculation. Pea and faba bean were inoculated with A. euteiches zoospores. Root colonization was examined. Root exudates from pea and faba bean were harvested and their impact on A. euteiches development were assessed by using in vitro assays. A. euteiches root colonization and the influence of the oomycete inoculation on specialized metabolites patterns and arabinogalactan protein (AGP) concentration of root exudates were also determined. In faba bean root, A. euteiches colonization was very low as compared with that of pea. Whereas infected pea root exudates have a positive chemotaxis index (CI) on zoospores, faba bean exudate CI was negative suggesting a repellent effect. While furanoacetylenic compounds were only detected in faba bean exudates, AGP concentration was specifically increased in pea.This work showed that early in the course of infection, host susceptibility to A. euteiches is involved via a plant-species specific root exudation opening new perspectives in pea root rot disease management.

International audience; Owing to their evolutionary potential, plant pathogens are able to rapidly adapt to genetically controlled plant resistance, often resulting in resistance breakdown and major epidemics in agricultural crops. Various deployment strategies have been proposed to improve resistance management. Globally, these rely on careful selection of resistance sources and their combination at various spatiotemporal scales (e.g., via gene pyramiding, crop rotations and mixtures, landscape mosaics). However, testing and optimizing these strategies using controlled experiments at large spatiotemporal scales are logistically challenging. Mathematical models provide an alternative investigative tool, and many have been developed to explore resistance deployment strategies under various contexts. This review analyzes 69 modeling studies in light of specific model structures (e.g., demographic or demogenetic, spatial or not), underlying assumptions (e.g., whether preadapted pathogens are present before resistance deployment), and evaluation criteria (e.g., resistance durability, disease control, cost-effectiveness). It highlights major research findings and discusses challenges for future modeling efforts.

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Background and Aims The necrotrophic fungus Botrytis cinerea infects a broad range of fruit crops including domesticated grapevine Vitis vinifera cultivars. Damage caused by this pathogen is severely detrimental to the table and wine grape industries and results in substantial crop losses worldwide. The apoplast and cell wall interface is an important setting where many plant–pathogen interactions take place and where some defence-related messenger molecules are generated. Limited studies have investigated changes in grape cell wall composition upon infection with B. cinerea, with much being inferred from studies on other fruit crops. Methods In this study, comprehensive microarray polymer profiling in combination with monosaccharide compositional analysis was applied for the first time to investigate cell wall compositional changes in the berries of wine (Sauvignon Blanc and Cabernet Sauvignon) and table (Dauphine and Barlinka) grape cultivars during Botrytis infection and tissue maceration. This was used in conjunction with scanning electron microscopy (SEM) and X-ray computed tomography (CT) to characterize infection progression. Key Results Grapes infected at veraison did not develop visible infection symptoms, whereas grapes inoculated at the post-veraison and ripe stages showed evidence of significant tissue degradation. The latter was characterized by a reduction in signals for pectin epitopes in the berry cell walls, implying the degradation of pectin polymers. The table grape cultivars showed more severe infection symptoms, and corresponding pectin depolymerization, compared with wine grape cultivars. In both grape types, hemicellulose layers were largely unaffected, as was the arabinogalactan protein content, whereas in moderate to severely infected table grape cultivars, evidence of extensin epitope deposition was present. Conclusions Specific changes in the grape cell wall compositional profiles appear to correlate with fungal disease susceptibility. Cell wall factors important in influencing resistance may include pectin methylesterification profiles, as well as extensin reorganization.

International audience; Drought-induced dehydration of vegetative tissues in lycopods affects growth and survival. Different species of Selaginella have evolved a series of specialized mechanisms to tolerate desiccation in vegetative tissues in response to water stress. In the present study, we report on the structural characterization of the leaf cell wall of the desiccation-tolerant species S. involvens and two desiccation-sensitive species, namely S. kraussiana and S. moellendorffii. Isolated cell walls from hydrated and desiccated leaves of each species were fractionated and the resulting oligosaccharide fragments were analyzed to determine their structural features. Our results demonstrate that desiccation induces substantial modifications in the cell wall composition and structure. Altogether, these data highlight the fact that structural remodeling of cell wall hemicellulosic polysaccharides including XXXG-rich xyloglucan, arabinoxylan and acetylated galactomannan is an important process in order to mitigate desiccation stress in Selaginella.

International audience; Interactions between neighbouring plants in an ecosystem can lead to competition, even in single-species stands. Genetic selection of perennial plants based on the individual values of genotypes does not usually take into account interactions that develop over time. The purpose of this study was to ascertain whether the effects of competition might affect the performance of cacao genotypes tested over long periods, and at what point those effects begin. Competition was studied on cacao trees (Theobroma cacao L) taking into account the diameter of the trees and their yields. The trial design set up in Côte d'Ivoire was a factorial mating design of the main cacao genetic improvement programme. The approach taken was a multivariate model based on 13 years of data gathering, including genetic, spatial and competition effects. The results revealed a gradual onset of competition starting in the early years of production up to the 4 th year, when its effect became significant. It first affected growth then, 2 years later, yields. Depending on the production years, the genetic effect and the spatial effect were the greatest. In years of strong competition, it could affect up to 10 % of the annual production variability, i.e. a quarter of the variability explained by genetics. The most vigorous trees always remained highly competitive and high-yielding. The competition effect will therefore always be substantial with selections of high-yielding individuals. "Group selection" of somewhat average, less competitive individuals would help to maximize yield gains through the combined performance of the group, rather than that of individual trees.

International audience; Plant disease phenotyping methodologies can vary considerably among testers and often suffer from shortcomings in their procedures and applications. This has been an important challenge in resistance breeding to brown rot, one of the most severe pre-and postharvest stone fruit diseases caused by Monilinia spp. Literature about methodologies for evaluating stone fruit susceptibility to brown rot is abundant but displays significant variations across the described approaches, limiting the ability to compare results from different studies. This is despite the fact that authors largely agree on the main factors influencing brown rot development, such as Monilinia inocula, environmental conditions, cultivars, fruit stage, and management practices. The present review first discusses ways to control or at least account for major factors affecting brown rot phenotyping studies. The second section describes in detail the different steps of fruit infection assays, comparing different protocols available in the literature with the objective of highlighting best practices and further improvement of phenotyping for brown rot susceptibility. Finally, experimental results from multi-year evaluation trials are also reported, highlighting year-to-year variability and exploring correlations of evaluation outcomes among years and assay types, suggesting that choice of phenotyping methodology must be carefully considered in breeding programs.

The diatomPhaeodactylum tricornutumis a marine unicellular microalga that exists under three main morphotypes: oval, fusiform, and triradiate. Previous works have demonstrated that the oval morphotype ofP. tricornutumPt3 strain presents specific metabolic features. Here, we compared the cellular organization of the main morphotypes of the diatomP. tricornutumPt3 strain through transmission electron and advanced light microscopies. The three morphotypes share similarities including spectral characteristics of the plastid, the location of the nucleus, the organization of mitochondria around the plastid as well as the existence of both a F-actin cortex, and an intracellular network of F-actin. In contrast, compared to fusiform and triradiate cells, oval cells spontaneously release proteins more rapidly. In addition, comparison of whole transcriptomes of oval versus fusiform or triradiate cells revealed numerous differential expression of positive and negative regulators belonging to the complex dynamic secretory machinery. This study highlights the specificities occurring within the oval morphotype underlying that the oval cells secrete proteins more rapidly.

Wood density is the product of carbon allocation for structural growth and reflects the trade-off between mechanical support and water conductivity. We tested a conceptual framework based on the assumption that micro-density depends on direct and indirect relationships with endogenous and exogenous factors. The dynamics of wood formation, including timings and rates of cell division, cell enlargement, and secondary wall deposition, were assessed from microcores collected weekly between 2002 and 2016 from five black spruce stands located along a latitudinal gradient in Quebec, Canada. Cell anatomy and micro-density were recorded by anatomical analyses and X-ray measurements. Our structural equation model explained 80% of micro-density variation within the tree-ring with direct effects of wall thickness (σ = 0.61), cell diameter (σ = -0.51), and photoperiod (σ = -0.26). Wood formation dynamics had an indirect effect on micro-density. Micro-density increased under longer periods of cell-wall deposition and shorter durations of enlargement. Our results fill a critical gap in understanding the relationships underlying micro-density variation in conifers. We demonstrated that short-term responses to environmental variations could be overridden by plastic responses that modulate cell differentiation. Our results point to wood formation dynamics as a reliable predictor of carbon allocation in trees.

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Hyperosmotic stresses represent some of the most serious abiotic factors that adversely affect plants growth, development and fitness. Despite their central role, the early cellular events that lead to plant adaptive responses remain largely unknown. In this study, using Arabidopsis thaliana cultured cells we analyzed early cellular responses to sorbitol-induced hyperosmotic stress. We observed biphasic and dual responses of A. thaliana cultured cells to sorbitol-induced hyperosmotic stress. A first set of events, namely singlet oxygen (1O2) production and cell hyperpolarization due to a decrease in anion channel activity could participate to signaling and osmotic adjustment allowing cell adaptation and survival. A second set of events, namely superoxide anion (O2-) production by RBOHD-NADPH-oxidases and SLAC1 anion channel activation could participate in programmed cell death (PCD) of a part of the cell population. This set of events raises the question of how a survival pathway and a death pathway could be induced by the same hyperosmotic condition and what could be the meaning of the induction of two different behaviors in response to hyperosmotic stress.

International audience; Secondary metabolites, such as phenolics, are plant defence substances. In the present study, the impact of Monilinia laxa inoculation under controlled conditions on phenolic content of apricot branches was investigated. A bi-parental hybrid population issued from Bergeron and Bakour cultivars (BerBa) and consisting of 192 hybrids was studied. The susceptibility of the BerBa population to M. laxa was evaluated by measuring the length of the necrosed tissues and the concentration of fungal DNA by qPCR in the branches 8 days post-inoculation. The results exhibit significant differences between the two parental cultivars in terms of necrosis length, which confirm their different susceptibility to the pathogen. A considerably high content of 2′,6′-dihydroxy-4′–methoxyacetophenone hexoside was found in branch tissues of Bakour (tolerant parental cultivar), amounting to 1.72 mg/g and 1.41 mg/g of fresh weight in non-inoculated and inoculated samples, respectively. The content of this compound in Bergeron branch tissues was several times lower, amounting to 0.24 mg/g and 0.14 mg/g of fresh weight in non-inoculated and inoculated samples, respectively. In the inoculated branches, scopolin was almost twice as abundant in the tolerant parental cultivar branch tissues as in the susceptible ones. In general, after inoculation a lower content of phenolic compounds was observed for hybrids with longer necrosed tissue. A Principal Component Analysis showed that at 8 days post-inoculation M. laxa concentration in the branches and the content of phenolic compounds, such as scopolin and chlorogenic acids, were negatively correlated. Additionally, the antifungal activity of pure phenolic compounds against M. laxa mycelial growth and spore germination was investigated. At a concentration of 500 mg/L, up to 40 % inhibition of M. laxa mycelial growth by scopoletin, up to 60 % inhibition by 2′,4′,6′-trihydroxyacetophenone and total inhibition by 2′-hydroxy-4′-methoxyacetophenone was observed. Scopoletin and 2′,4′,6′-trihydroxyacetophenone also inhibited spore germination by about 50 %. These results can serve to improve breeding programs aiming to develop apricot cultivars resistant to brown rot blossom blight.

Background: Nitrogen fertilization is known to increase disease susceptibility, a phenomenon called Nitrogen-Induced Susceptibility (NIS). In rice, this phenomenon has been observed in infections with the blast fungus Magnaporthe oryzae. A previous classical genetic study revealed a locus (NIS1) that enhances susceptibility to rice blast under high nitrogen fertilization. In order to further address the underlying genetics of plasticity in susceptibility to rice blast after fertilization, we analyzed NIS under greenhouse-controlled conditions in a panel of 139 temperate japonica rice strains. A genome-wide association analysis was conducted to identify loci potentially involved in NIS by comparing susceptibility loci identified under high and low nitrogen conditions, an approach allowing for the identification of loci validated across different nitrogen environments. We also used a novel NIS Index to identify loci potentially contributing to plasticity in susceptibility under different nitrogen fertilization regimes.Results: A global NIS effect was observed in the population, with the density of lesions increasing by 8%, on average, under high nitrogen fertilization. Three new QTL, other than NIS1, were identified. A rare allele of the RRobN1 locus on chromosome 6 provides robust resistance in high and low nitrogen environments. A frequent allele of the NIS2 locus, on chromosome 5, exacerbates blast susceptibility under the high nitrogen condition. Finally, an allele of NIS3, on chromosome 10, buffers the increase of susceptibility arising from nitrogen fertilization but increases global levels of susceptibility. This allele is almost fixed in temperate japonicas, as a probable consequence of genetic hitchhiking with a locus involved in cold stress adaptation.Conclusions: Our results extend to an entire rice subspecies the initial finding that nitrogen increases rice blast susceptibility. We demonstrate the usefulness of estimating plasticity for the identification of novel loci involved in the response of rice to the blast fungus under different nitrogen regimes.

International audience; exDNA is found in various organisms, including plants. However, plant exDNA has thus far received little attention related to its origin and role in the RET (root extracellular trap). In this study, we performed the first high-throughput genomic sequencing of plant exDNA from a Fabaceae with worldwide interest: soybean (Glycine max (L.) Merr.). The origin of this exDNA was first investigated in control condition, and the results show high-coverage on organelles (mitochondria/plastid) DNA relative to nuclear DNA, as well as a mix of coding and non-coding sequences. In the second part of this study, we investigated if exDNA release was modified during an elicitation with PEP-13 (a peptide elicitor from oomycete genus Phytophthora). Our results show that treatment of roots with PEP-13 does not affect the composition of exDNA.

Ce volume regroupe les textes issus du programme Casdar « Semence et Sélection Variétale » finalisés en 2015, 2017 et 2019. Le numéro a été coordonné par le Comité Scientifique du Comité Technique Permanent de la Sélection des plantes cultivées (CTPS).Qualité sanitaire des semences et plants; 'Candidatus Liberibacter solanacearum' (Lso) is the phloem bacterium responsible for the "Zebra Chip"disease in the USA. In France, it was reported for the first time in 2012 on seed carrots. The CaLisoproject validated a Lso detection method and thus made the health quality of carrot seeds reliable andguaranteed the same reliability for potato plants. In France, our large-scale surveys show that the LsoDand LsoE haplotypes are present in the majority of Apiaceae production areas, and that Bactericeratrigonica is the main psyllid species present on these crops. This psyllid is probably the main vector ofLso in France. In addition, Lso was not detected on potatoes, especially those produced near Apiaceaecrops, which underlines the very low risk of Lso transmission from carrots to potatoes. The studies carried out improved our knowledge of this pathosystem. Lso does not seem to be emerging on Apiaceae inFrance. The major threat for Solanaceae would probably be an introduction of the potato psyllid, B.cockerelli, in Europe.; ‘Candidatus Liberibacter solanacearum’ (Lso) est la bactérie du phloème responsable de la maladie du« Zebra Chip » aux USA. En France, elle a été signalée pour la première fois en 2012 sur carotte portegraine. Le projet CaLiso a permis de valider une méthode de détection de Lso et donc de fiabiliser laqualité sanitaire des semences de carotte et de garantir celle des plants de pomme de terre. En France,les prospections à grande échelle montrent que les haplotypes LsoD et LsoE sont présents dans lamajorité des zones de productions d’apiacées et que Bactericera trigonica est la principale espèce depsylles présente sur ces cultures. Ce psylle constitue probablement le principal vecteur de Lso en France.De plus, Lso n’a pas été détectée sur pommes de terre, notamment celles produites à proximité decultures d’apiacées, ce qui souligne le très faible risque de transmission de Lso de la carotte vers lapomme de terre. Les études menées ont permis de mieux connaitre ce pathosystème. Lso ne semblepas émergente sur apiacées en France mais pourrait l’être sur solanacées (haplotypes A et B) en casd’introduction du psylle de la pomme de terre, B. cockerelli, en Europe.

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We performed a genome‐wide association study of pepper (Capsicum annuum) tolerance to potato virus Y (PVY). For 254 pepper accessions, we estimated the tolerance to PVY as the coefficient of regression of the fresh weight (or height) of PVY‐infected and mock‐inoculated plants against within‐plant virus load. Small (strongly negative) coefficients of regression indicate low tolerance because plant biomass or growth decreases sharply as virus load increases. The tolerance level varied largely, with some pepper accessions showing no symptoms or fairly mild mosaics, whereas about half (48%) of the accessions showed necrotic symptoms. We found two adjacent single‐nucleotide polymorphisms (SNPs) at one extremity of chromosome 9 that were significantly associated with tolerance to PVY. Similarly, in three biparental pepper progenies, we showed that the induction of necrosis on PVY systemic infection segregated as a monogenic trait determined by a locus on chromosome 9. Our results also demonstrate the existence of a negative correlation between resistance and tolerance among the cultivated pepper accessions at both the phenotypic and genetic levels. By comparing the distributions of the tolerance‐associated SNP alleles and previously identified PVY resistance‐associated SNP alleles, we showed that cultivated pepper accessions possess favourable alleles for both resistance and tolerance less frequently than expected under random associations, while the minority of wild pepper accessions frequently combined resistance and tolerance alleles. This divergent evolution of PVY resistance and tolerance could be related to pepper domestication or farmer's selection., Among a core‐collection of pepper accessions, phenotypic and genetic negative correlations were found between resistance and tolerance to PVY for the cultivated pepper accessions, but not for the wild pepper accessions.

In Normandy, flax is a plant of important economic interest because of its fibres. Fusarium oxysporum, a telluric fungus, is responsible for the major losses in crop yield and fibre quality. Several methods are currently used to limit the use of phytochemicals on crops. One of them is the use of plant growth promoting rhizobacteria (PGPR) occurring naturally in the rhizosphere. PGPR are known to act as local antagonists to soil-borne pathogens and to enhance plant resistance by eliciting the induced systemic resistance (ISR). In this study, we first investigated the cell wall modifications occurring in roots and stems after inoculation with the fungus in two flax varieties. First, we showed that both varieties displayed different cell wall organization and that rapid modifications occurred in roots and stems after inoculation. Then, we demonstrated the efficiency of a Bacillus subtilis strain to limit Fusarium wilt on both varieties with a better efficiency for one of them. Finally, thermo-gravimetry was used to highlight that B. subtilis induced modifications of the stem properties, supporting a reinforcement of the cell walls. Our findings suggest that the efficiency and the mode of action of the PGPR B. subtilis is likely to be flax variety dependent.

International audience; Three viruses transmitted by aphids (non-persistent transmission) are responsible of strong yield losses on squash crops in France and around the world: Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV) and Watermelon mosaic virus (WMV). For each virus, different biological, serological and molecular groups were described. The resistance is polygenic for CMV, ZYMV and with a major gene for WMV but always with an intermediate resistance.The evaluation of squash resistance to viruses and the assessment of symptoms are complex due to the partial and not complete resistance and the quantitative results observed. It is important to describe the different levels of virulence of virus strains and to identify the different levels of resistance of squash varieties. There are currently no harmonized protocols to define the levels of partial resistance of squash to these viruses.The aim of this project, in collaboration between GEVES, INRAE and breeding companies (HMClause, Gautier, Monsanto, Rijk Zwaan, Sakata, Syngenta) was to acquire a better knowledge of levels of squash resistance and to define robust resistance tests to these viruses. Based on the INRAE’s characterized collection of strains of viruses, three strains per virus (with different virulences and from different groups) were selected. These strains and different protocols from INRAE and partners (stage of inoculation, optimal conditions of test, notation scale) were compared, on a panel of commercial varieties with different levels of resistance, to define for each virus a robust resistance test.One strain per virus, making it possible to differentiate the different levels of resistance of varieties, was selected. For each virus, a resistance test and reference materials (strain and controls) were validated. The reference collection of GEVES was characterized for the three viruses. These new protocols, used for CTPS registration, will be proposed to CPVO and UPOV for a harmonized use.; Trois virus transmis par les pucerons selon le mode non-persistant sont responsables d’importantes pertes de récolte dans les cultures de courgette en France et dans le monde : les Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV) et Watermelon mosaic virus (WMV)L’évaluation de la résistance de la courgette aux virus est complexe du fait du caractère partiel (ou non complet) de la résistance et des résultats quantitatifs observés. Il est important d’identifier les différents niveaux de résistance des variétés de courgette à ces virus, et de décrire les niveaux d’agressivité des souches permettant de mieux différencier les variétés. Actuellement, il n’existe pas de protocole harmonisé pour définir les différents niveaux de résistance partielle de la courgette à ces virus.Le but de ce projet collaboratif entre le GEVES, l’INRAE et des sociétés semencières (HMClause, Gautier, Monsanto, Rijk Zwaan, Sakata, Syngenta) était d’acquérir de meilleures connaissances des niveaux de résistance de la courgette et de définir un protocole de test robuste pour ces virus. Basée sur la collection de souches de virus caractérisée par INRAE, trois souches par virus (avec différentes agressivités et appartenant à différents groupes) ont été sélectionnées. Ces souches et les différents protocoles de INRAE et des partenaires (stade d’inoculation, conditions optimales de test, échelle de notation) ont été comparées sur un panel composé de variétés commerciales avec différents niveaux de résistance afin de définir pour chaque virus un test de résistance robuste.Une souche, permettant de différencier les différents niveaux de résistance des variétés, a été sélectionnée par virus. Pour chaque virus, un test de résistance et le matériel de référence (souches et témoins) ont été validés. La collection de référence du GEVES a été caractérisée pour les trois virus. Ces nouveaux protocoles, utilisés pour les

Theo Mauri,1 Laurence Menu-Bouaouiche,2 Muriel Bardor,2 Tony Lefebvre,1 Marc F Lensink,1 Guillaume Brysbaert1 1Univ. Lille, CNRS; UMR8576 - UGSF - Unité de Glycobiologie Structurale et Fonctionnelle, Lille, F-59000, France; 2Normandy University, UNIROUEN, Laboratoire Glyco-MEV EA4358, Rouen, 76000, FranceCorrespondence: Theo Mauri; Guillaume BrysbaertUGSF Campus CNRS, Parc de la haute-borne, 50 Avenue de Halley, BP 70478, 59658 Villeneuve d’Ascq Cédex, Lille, FranceTel +33 3 62 53 17 32Fax +33 3 62 53 17 01Email theo.mauri@univ-lille.fr; guillaume.brysbaert@univ-lille.frBackground: O-GlcNAcylation is an essential post-translational modification (PTM) in mammalian cells. It consists in the addition of a N-acetylglucosamine (GlcNAc) residue onto serines or threonines by an O-GlcNAc transferase (OGT). Inhibition of OGT is lethal, and misregulation of this PTM can lead to diverse pathologies including diabetes, Alzheimer’s disease and cancers. Knowing the location of O-GlcNAcylation sites and the ability to accurately predict them is therefore of prime importance to a better understanding of this process and its related pathologies.Purpose: Here, we present an evaluation of the current predictors of O-GlcNAcylation sites based on a newly built dataset and an investigation to improve predictions.Methods: Several datasets of experimentally proven O-GlcNAcylated sites were combined, and the resulting meta-dataset was used to evaluate three prediction tools. We further defined a set of new features following the analysis of the primary to tertiary structures of experimentally proven O-GlcNAcylated sites in order to improve predictions by the use of different types of machine learning techniques.Results: Our results show the failure of currently available algorithms to predict O-GlcNAcylated sites with a precision exceeding 9%. Our efforts to improve the precision with new features using machine learning techniques do succeed for equal proportions of O-GlcNAcylated and non-O-GlcNAcylated sites but fail like the other tools for real-life proportions where ∼ 1.4% of S/T are O-GlcNAcylated.Conclusion: Present-day algorithms for O-GlcNAcylation prediction narrowly outperform random prediction. The inclusion of additional features, in combination with machine learning algorithms, does not enhance these predictions, emphasizing a pressing need for further development. We hypothesize that the improvement of prediction algorithms requires characterization of OGT’s partners.Keywords: machine learning, glycosylation, O-GlcNAc, post-translational modification, dataset, OGT

International audience; Clubroot is an important root disease of canola/oilseed rape (Brassica napus L.) caused by Plasmodiophora brassicae. To cope with the emergence of new virulent pathotypes of P. brassicae that threaten canola production in western Canada, there is a need to identify novel sources of resistance for breeding programmes. In the present study, a series of nine B. napus genotypes, from different geographic origins, were screened for resistance to Canadian single-spore and field isolates of P. brassicae. The effect of nitrogen fertilization on the resistance level of these genotypes was also evaluated. Under full nitrogen fertilization, several of the tested host genotypes harboured isolate-specific partial resistance to P. brassicae infection, with some of these interactions resulting in disease indices P. brassicae also were identified. The influence of nitrogen on the level of resistance varied according to the specific plant genotype/pathogen isolate combination. Under low nitrogen fertilization, the genotype 'Darmor-bzh' showed a high level of partial resistance to isolates belonging to pathotypes 2 and 3, and 'Express' and 'Grouse' showed resistance to pathotype 2. The results confirm that nitrogen fertilization is an important factor to consider in combination with the use of resistant varieties for the management of clubroot.

Master; In poplars, varietal improvement is based on the valorisation of interspecific hybrids in the form of clones resulting from the combination of the Eurasian species Populus nigra L. with P. deltoides, a poplar native to North America. The Eurasian parent has a good behaviour with regard to leaf rust (Melampsora larici-populina, Mlp), this native species coevolving with the populations of the pathogen. However, we found a strong Genotype x Strain interaction for partial resistance in P. nigra, and we identified specific effect QTLs according to the Mlp strain used. In a context of development of cultivars with durable resistance, it is essential to consider these interactions. One of the strategies is to consider the behaviour of each individual to several strains and thus define a reaction norm that can be the target of selection. In the end, such a characterization would make it possible to propose a cocktail of poplar genotypes covering all the resistances.Reaction norms are a mean of describing the plasticity of organisms to their environment (Sanchez et al., 2013). They are often modelled (in the form of a function) according to gradients of a continuous environmental variable (temperature, light, water availability ... Marchal et al., 2019). Very few studies have focused on characterizing pest gradients. The proposed research work is part of the European B4EST project (http://b4est.eu/).The objectives are:- To develop reaction norms to describe the interaction Black Poplar / Mlp. For this, pathological tests under controlled conditions will be performed on a set of families (300 individuals) against 7 Mlp strains. These strains are already characterized and highlight GxS interactions on a collection of 26 P. nigra genotypes from natural populations.- To elucidate the genetic control of these standards through GWAS (Genome Wide Association Study) using parameters describing the reaction norms.

Two environmentally stable QTLs linked to black spot disease resistance in the Rosa wichurana genetic background were detected, in different connected populations, on linkage groups 3 and 5. Co-localization between R-genes and defense response genes was revealed via meta-analysis. The widespread rose black spot disease (BSD) caused by the hemibiotrophic fungus Diplocarpon rosae Wolf. is efficiently controlled with fungicides. However, in the actual context of reducing agrochemical use, the demand for rose bushes with higher levels of resistance has increased. Qualitative resistance conferred by major genes (Rdr genes) has been widely studied but quantitative resistance to BSD requires further investigation. In this study, segregating populations connected through the BSD resistant Rosa wichurana male parent were phenotyped for disease resistance over several years and locations. A pseudo-testcross approach was used, resulting in six parental maps across three populations. A total of 45 individual QTLs with significant effect on BSD resistance were mapped on the male maps (on linkage groups (LG) B3, B4, B5 and B6), and 12 on the female maps (on LG A1, A2, A3, A4 and A5). Two major regions linked to BSD resistance were identified on LG B3 and B5 of the male maps and were integrated into a consensus map built from all three of the male maps. A meta-analysis was used to narrow down the confidence intervals of individual QTLs from three populations by generating meta-QTLs. Two 'hot spots' or meta-QTLs were found per LG, enabling reduction of the confidence interval to 10.42 cM for B3 and 11.47 cM for B5. An expert annotation of NBS-LRR encoding genes of the genome assembly of Hibrand et al. was performed and used to explore potential co-localization with R-genes. Co-localization with defense response genes was also investigated.

Background Extensins are plant cell wall hydroxyproline-rich glycoproteins known to be involved in cell wall reinforcement in higher plants, and in defence against pathogen attacks. The ability of extensins to form intra- and intermolecular cross-links is directly related to their role in cell wall reinforcement. Formation of such cross-links requires appropriate glycosylation and structural conformation of the glycoprotein. Scope Although the role of cell wall components in plant defence has drawn increasing interest over recent years, relatively little focus has been dedicated to extensins. Nevertheless, new insights were recently provided regarding the structure and the role of extensins and their glycosylation in plant–microbe interactions, stimulating an interesting debate from fellow cell wall community experts. We have previously revealed a distinct distribution of extensin epitopes in Arabidopsis thaliana wild-type roots and in mutants impaired in extensin arabinosylation, in response to elicitation with flagellin 22. That study was recently debated in a Commentary by Tan and Mort (Tan L, Mort A. 2020. Extensins at the front line of plant defence. A commentary on: ‘Extensin arabinosylation is involved in root response to elicitors and limits oomycete colonization’. Annals of Botany 125: vii–viii) and several points regarding our results were discussed. As a response, we herein clarify the points raised by Tan and Mort, and update the possible epitope structure recognized by the anti-extensin monoclonal antibodies. We also provide additional data showing differential distribution of LM1 extensin epitopes in roots between a mutant defective in PEROXIDASES 33 and 34 and the wild type, similarly to previous observations from the rra2 mutant defective in extensin arabinosylation. We propose these two peroxidases as potential candidates to specifically catalyse the cross-linking of extensins within the cell wall. Conclusions Extensins play a major role within the cell wall to ensure root protection. The cross-linking of extensins, which requires correct glycosylation and specific peroxidases, is most likely to result in modulation of cell wall architecture that allows enhanced protection of root cells against invading pathogens. Study of the relationship between extensin glycosylation and their cross-linking is a very promising approach to further understand how the cell wall influences root immunity.

International audience; Plants are surrounded by a diverse range of microorganisms that causes serious crop losses and requires the use of pesticides. Flax is a major crop in Normandy used for its fibres and is regularly challenged by the pathogenic fungus Fusarium oxysporum (Fo) f. sp. lini. To protect themselves, plants use "innate immunity" as a first line of defense level against pathogens. Activation of plant defense with elicitors could be an alternative for crop plant protection. A previous work was conducted by screening a chemical library and led to the identification of compounds able to activate defense responses in Arabidopsis thaliana. Four compounds were tested for their abilities to improve resistance of two flax varieties against Fo. Two of them, one natural (holaphyllamine or HPA) and one synthetic (M4), neither affected flax nor Fo growth. HPA and M4 induced oxidative burst and callose deposition. Furthermore, HPA and M4 caused changes in the expression patterns of defense-related genes coding a glucanase and a chitinase-like. Finally, plants pre-treated with HPA or M4 exhibited a significant decrease in the disease symptoms. Together, these findings demonstrate that HPA and M4 are able to activate defense responses in flax and improve its resistance against Fo infection.

International audience; Oil palm is an oil-producing crop of major importance at the global scale. Oil palm mesocarp lipids are used for myriads industrial applications, and market demand has been growing for decades. In addition, oil palm seeds are oleaginous, and the oil extracted therefrom can be used for several purposes, from food to cosmetics. As such, there is a huge need in oil palm seeds to maintain the global cohort of more than 2 billion trees. However, oil palm seed germination is a rather difficult process, not only to break dormancy, but also because it is long and often reaches lower-than-expected germination rates. Surprisingly, despite the crucial importance of germination for oil palm plantation management, our knowledge is still rather limited, in particular about germinating oil palm seed metabolism. The present review incorporates different pieces of information that have been obtained in the past few years, in oil palm and in other palm species, in order to provide an overview of germination metabolism and its control. Further insights can also be gained from other oleaginous model plants, such as Arabidopsis or canola, however, palm seeds have peculiarities that must be accounted for, to gain a better understanding of germinating seed metabolism.

Plant virus pathogenicity is expected to vary with changes in the abiotic environment that affect plant physiology. Conversely, viruses can alter the host plant response to additional stimuli from antagonism to mutualism depending on the virus, the host plant and the environment. Ecological theory, specifically the CSR framework of plant strategies developed by Grime and collaborators, states that plants cannot simultaneously optimize resistance to both water deficit and pathogens. Here, we investigated the vegetative and reproductive performance of 44 natural accessions of A. thaliana originating from the Iberian Peninsula upon simultaneous exposure to soil water deficit and viral infection by the Cauliflower mosaic virus (CaMV). Following the predictions of Grime’s CSR theory, we tested the hypothesis that the ruderal character of a plant genotype is positively related to its tolerance to virus infection regardless of soil water availability. Our results showed that CaMV infection decreased plant vegetative performance and annihilated reproductive success of all accessions. In general, water deficit decreased plant performance, but, despite differences in behavior, ranking of accessions tolerance to CaMV was conserved under water deficit. Ruderality, quantified from leaf traits following a previously published procedure, varied significantly among accessions, and was positively correlated with tolerance to viral infection under both well-watered and water deficit conditions, although the latter to a lesser extent. Also, in accordance with the ruderal character of the accession and previous findings, our results suggest that accession tolerance to CaMV infection is positively correlated with early flowering. Finally, plant survival to CaMV infection increased under water deficit. The complex interactions between plant, virus and abiotic environment are discussed in terms of the variation in plant ecological strategies at the intraspecific level., Author summary Virus pathogenicity may be influenced by changes in the abiotic environment. A common change is decrease in soil water availability, which is detrimental to plant productivity and the occurrence of which is expected to increase due to climate change, has recently been shown to interfere with plant–virus interactions. We investigated the performance of 44 natural accessions of the plant species Arabidopsis thaliana infected by Cauliflower mosaic virus under well-watered and water deficit conditions. We showed that viral infection decreased plant vegetative performance and annihilated reproductive success of all accessions, and that these pathogenic effects were increased by water deficit. Intrinsic characteristics of the accessions were related to their tolerance to the virus so that accessions with low leaf tissue density and rapid growth rate were more tolerant to viral infection regardless of watering condition. Finally, plant survival upon viral infection increased under water deficit. We discuss the role of intrinsic plant characteristics, seen as ecological strategies, in plant tolerance to viral infections under contrasting environmental conditions, and the consequences for the study of viral epidemiology.

Xylella fastidiosa is one of the most important threats to plant health worldwide, causing disease in the Americas on a range of agricultural crops and trees, and recently associated with a critical epidemic affecting olive trees in Europe. A main challenge for the detection of the pathogen and the development of physiological studies is its fastidious growth, as the generation time can vary from 10 to 100 h for some strains. This physiological peculiarity is shared with several human pathogens and is poorly understood. We performed an analysis of the metabolic capabilities of X. fastidiosa through a genome-scale metabolic model of the bacterium. This model was reconstructed and manually curated using experiments and bibliographical evidence. Our study revealed that fastidious growth most probably results from different metabolic specificities such as the absence of highly efficient enzymes or a global inefficiency in virulence factor production. These results support the idea that the fragility of the metabolic network may have been shaped during evolution to lead to the self-limiting behavior of X. fastidiosa., High proliferation rate and robustness are vital characteristics of bacterial pathogens that successfully colonize their hosts. The observation of drastically slow growth in some pathogens is thus paradoxical and remains unexplained. In this study, we sought to understand the slow (fastidious) growth of the plant pathogen Xylella fastidiosa. Using genome-scale metabolic network reconstruction, modeling, and experimental validation, we explored its metabolic capabilities. Despite genome reduction and slow growth, the pathogen’s metabolic network is complete but strikingly minimalist and lacking in robustness. Most alternative reactions were missing, especially those favoring fast growth, and were replaced by less efficient paths. We also found that the production of some virulence factors imposes a heavy burden on growth. Interestingly, some specific determinants of fastidious growth were also found in other slow-growing pathogens, enriching the view that these metabolic peculiarities are a pathogenicity strategy to remain at a low population level. IMPORTANCE Xylella fastidiosa is one of the most important threats to plant health worldwide, causing disease in the Americas on a range of agricultural crops and trees, and recently associated with a critical epidemic affecting olive trees in Europe. A main challenge for the detection of the pathogen and the development of physiological studies is its fastidious growth, as the generation time can vary from 10 to 100 h for some strains. This physiological peculiarity is shared with several human pathogens and is poorly understood. We performed an analysis of the metabolic capabilities of X. fastidiosa through a genome-scale metabolic model of the bacterium. This model was reconstructed and manually curated using experiments and bibliographical evidence. Our study revealed that fastidious growth most probably results from different metabolic specificities such as the absence of highly efficient enzymes or a global inefficiency in virulence factor production. These results support the idea that the fragility of the metabolic network may have been shaped during evolution to lead to the self-limiting behavior of X. fastidiosa.

Seed dormancy and timing of its release is an important developmental transition determining the survival of individuals, populations, and species in variable environments. Medicago truncatula was used as a model to study physical seed dormancy at the ecological and genetics level. The effect of alternating temperatures, as one of the causes releasing physical seed dormancy, was tested in 178 M. truncatula accessions over three years. Several coefficients of dormancy release were related to environmental variables. Dormancy varied greatly (4&ndash, 100%) across accessions as well as year of experiment. We observed overall higher physical dormancy release under more alternating temperatures (35/15 &deg, C) in comparison with less alternating ones (25/15 &deg, C). Accessions from more arid climates released dormancy under higher experimental temperature alternations more than accessions originating from less arid environments. The plasticity of physical dormancy can probably distribute the germination through the year and act as a bet-hedging strategy in arid environments. On the other hand, a slight increase in physical dormancy was observed in accessions from environments with higher among-season temperature variation. Genome-wide association analysis identified 136 candidate genes related to secondary metabolite synthesis, hormone regulation, and modification of the cell wall. The activity of these genes might mediate seed coat permeability and, ultimately, imbibition and germination.

Key message New genotypes of hybrid poplars from theAigeirosandTacamahacasections have great potential for increasing genetic gain from selection. The most promising traits are associated with productivity and resistance toSphaerulina musiva-induced canker while wood density can be selected for secondarily. A minimum age of 8 years is reliable to select fast-growing resistant clones in northern climates. Context Productivity, wood density, and disease resistance of hybrid poplar clones are important traits when selecting for cultivation at an industrial scale. Aims We studied 1978 hybrid poplar clones from 63 families, bred from poplars native (Populus balsamifera and Populus deltoides) and non-native to Canada from the Aigeiros and Tacamahaca sections, to improve economically important traits for plantations in northern Alberta. Methods Genetic parameters for diameter at breast height (DBH), height, resistance to Sphaerulina musiva-induced canker, and wood density were determined up to age 10. Results A mean annual increment of 16.5 m3 ha−1 year−1 was achieved at age 10 in the best-performing clones. The potential genetic gain for DBH, height, and canker resistance, 37%, 26%, and ~ 13%, respectively, was achieved when selecting the top 10% of the tested clones. The genetic effect for wood density was weak. The age-age genetic correlations identified age eight as a reliable selection age. Conclusion The new hybrid poplar clones tested exhibited great potential for tree improvement. The next phase of selection should test a reduced number of clones on different site types, identifying stable clones for productivity and resistance, while wood density can be selected for secondarily. In northern regions, a minimum age of 8 years is reliable to select fast-growing resistant clones for commercial deployment.

International audience; Plants can provide a cost-effective and scalable technology for production of therapeutic monoclonal antibodies, with the potential for precise engineering of glycosylation. Glycan structures in the antibody Fc region influence binding properties to Fc receptors, which opens opportunities for modulation of antibody effector functions. To test the impact of glycosylation in detail, on binding to human Fc receptors, different glycovariants of VRC01, a broadly neutralizing HIV monoclonal antibody, were generated in Nicotiana benthamiana and characterized. These include glycovariants lacking plant characteristic a1,3-fucose and b1,2-xylose residues and glycans extended with terminal b1,4-galactose. Surface plasmon resonance-based assays were established for kinetic/affinity evaluation of antibody-FccR interactions, and revealed that antibodies with typical plant glycosylation have a limited capacity to engage FccRI, FccRIIa, FccRIIb and FccRIIIa; however, the binding characteristics can be restored and even improved with targeted glycoengineering. All plant-made glycovariants had a slightly reduced affinity to the neonatal Fc receptor (FcRn) compared with HEK cell-derived antibody. However, this was independent of plant glycosylation, but related to the oxidation status of two methionine residues in the Fc region. This points towards a need for process optimization to control oxidation levels and improve the quality of plant-produced antibodies.

Made available in DSpace on 2020-12-12T02:09:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-06-01 Plants produce a vast array of defense compounds to protect themselves from pathogen attack or herbivore predation. Saponins are a specific class of defense compounds comprising bioactive glycosides with a steroidal or triterpenoid aglycone backbone. The model legume Medicago truncatula synthesizes two types of saponins, hemolytic saponins and nonhemolytic soyasaponins, which accumulate as specific blends in different plant organs. Here, we report the identification of the seed-specific transcription factor TRITERPENE SAPONIN ACTIVATION REGULATOR3 (TSAR3), which controls hemolytic saponin biosynthesis in developing M. truncatula seeds. Analysis of genes that are coexpressed with TSAR3 in transcriptome data sets from developing M. truncatula seeds led to the identification of CYP88A13, a cytochrome P450 that catalyzes the C-16a hydroxylation of medicagenic acid toward zanhic acid, the final oxidation step of the hemolytic saponin biosynthesis branch in M. truncatula. In addition, two uridine diphosphate glycosyltransferases, UGT73F18 and UGT73F19, which glucosylate hemolytic sapogenins at the C-3 position, were identified. The genes encoding the identified biosynthetic enzymes are present in clusters of duplicated genes in the M. truncatula genome. This appears to be a common theme among saponin biosynthesis genes, especially glycosyltransferases, and may be the driving force of the metabolic evolution of saponins. Ghent University Department of Plant Biotechnology and Bioinformatics VIB Center for Plant Systems Biology Department of Organic Chemistry Institute of Chemistry São Paulo State University (UNESP) Institut de Recherche en Horticulture et Semences-Unités Mixtes de Recherche Université d’Angers INRAE Institut Agro, SFR 4207 QuaSaV VIB Metabolomics Core Department of Organic Chemistry Institute of Chemistry São Paulo State University (UNESP)

International audience; Root border cells (BCs) and their associated secretions form a protective structure termed the root extracellular trap (RET) that plays a major role in root interactions with soil borne microorganisms. In this study, we investigated the release and morphology of BCs of Glycine max using light and cryo-scanning electron microscopy (SEM). We also examined the occurrence of cell-wall glycomolecules in BCs and secreted mucilage using immunofluorescence microscopy in conjunction with anti-glycan antibodies. Our data show that root tips released three populations of BCs defined as spherical, intermediate and elongated cells. The mechanism of shedding seemed to be cell morphotype-specific. The data also show that mucilage contained pectin, cellulose, extracellular DNA, histones and two hemicellulosic polysaccharides, xyloglucan and heteromannan. The latter has never been reported previously in any plant root secretions. Both hemicellulosic polysaccharides formed a dense fibrillary network embedding BCs and holding them together within the mucilage. Finally, we investigated the effect of the RET on the interactions of root with the pathogenic oomycete Phytophthora parasitica early during infection. Our findings reveal that the RET prevented zoospores from colonizing root tips by blocking their entry into root tissues and inducing their lysis.

© 2020 by the authors., Identification of sequence types (ST) of Xylella fastidiosa based on direct MultiLocus Sequence Typing (MLST) of plant DNA samples is partly efficient. In order to improve the sensitivity of X. fastidiosa identification, we developed a direct nested-MLST assay on plant extracted DNA. This method was performed based on a largely used scheme targeting seven housekeeping gene (HKG) loci (cysG, gltT, holC, leuA, malF, nuoL, petC). Samples analyzed included 49 plant species and two insect species (Philaenus spumarius, Neophilaenus campestris) that were collected in 2017 (106 plant samples in France), in 2018 (162 plant samples in France, 40 plant samples and 26 insect samples in Spain), and in 2019 (30 plant samples in Spain). With the nested approach, a significant higher number of samples were amplified. The threshold was improved by 100 to 1000 times compared to conventional PCR. Using nested-MLST assay, plants that were not yet considered hosts tested positive and revealed novel alleles in France, whereas for Spanish samples it was possible to assign the subspecies or ST to samples considered as new hosts in Europe. Direct typing by nested-MLST from plant material has an increased sensitivity and may be useful for epidemiological purposes., ED salary was funded by INRA SPE division and Anses. This work received support from the European Union’s Horizon 2020 research and innovation program under grant agreement 727987 XF-ACTORS (Xylella fastidiosa Active Containment Through a multidisciplinary-Oriented Research Strategy), and from Projects E-RTA2017-00004-C06-02 from ‘Programa Estatal de I+D Orientada a los Retos de la Sociedad’ from Spanish State Research Agency and from the Organización Interprofesional del Aceite de Oliva Español, CSIC Intramural Project 2018 40E111, and from “Conselleria de Agricultura, Desarrollo Rural, Emergencia Climática y Transición Ecológica” from Valencia region, and the Ministry of Agriculture, Fisheries and Food of Spain. The present work reflects only the authors’view and the EU funding agency is not responsible for any use that may be made of the information it contains.